1. Field of the Invention
The present invention relates to a fuel cell system and, more particularly, to a reformer having an improved heat transfer structure.
2. Description of the Related Art
As is well known, a fuel cell is an electricity generating system for directly converting chemical reaction energy of oxygen and hydrogen contained in a hydrocarbon fuel into electrical energy.
Fuel cells can be classified into polymer electrolyte membrane fuel cells and direct oxidation membrane fuel cells.
The polymer electrolyte membrane fuel cell has been recently developed to have excellent output characteristics, low operating temperatures, and fast starting and response characteristics. Therefore, the polymer electrolyte membrane fuel cell has a wide range of applications, including mobile power sources for vehicles, distributed power sources for homes or other buildings, and small-size power sources for electronic apparatuses.
The polymer electrolyte membrane fuel cell system includes a fuel cell body (hereinafter, referred to as a stack), a reformer for reforming a fuel to generate hydrogen and for supplying the hydrogen to the stack, and an air pump, or a fan, for supplying oxygen to the stack. The stack generates electrical energy through an electrochemical reaction between the hydrogen supplied from the reformer and the oxygen supplied by driving the air pump or the fan.
In the conventional fuel cell system, the reformer includes a heat source unit for providing thermal energy in a predetermined temperature range by using exothermic and endothermic reactions with catalysts, a reforming reaction unit for generating reforming gas (i.e., hydrogen-rich gas) from a fuel through a reforming reaction by using the thermal energy, and a carbon monoxide reducing unit for reducing a concentration of carbon monoxide contained in the reforming gas.
However, in the conventional reformer, the heat source unit and the reforming reaction unit are disposed in a distributed manner to transfer the thermal energy generated from the heat source unit to the reforming reaction unit (i.e., the heat source unit and the reforming reaction unit are provided separately). Therefore, in the conventional reformer, the exchange of thermal energy between the heat source and the reforming reaction unit is not directly performed, so that there is a problem in terms of thermal transfer efficiency. In particular, since the heat source unit transfers the thermal energy from outside of the reforming reaction unit to the reforming reaction unit, the thermal energy is not completely transferred to the reforming reaction unit but, instead, is partially released to the outside. Therefore, there is a problem of deterioration in reaction efficiency and thermal efficiency of the entire reformer. In addition, in the conventional reformer, since the heat source unit and the reforming reaction unit are disposed in a distributed manner, there is a problem in that the entire system is not compact.
In addition, in the conventional reformer, optimal operation efficiency can be obtained only if the thermal energy is in a temperature range that corresponds to specific temperatures of the reforming reaction unit and the carbon monoxide reducing unit. However, the transfer of the thermal energy to the reforming reaction unit and the carbon monoxide reducing unit cannot be easily controlled, so that there is a problem in that it is difficult to maximize the operation efficiency of the entire reformer.